The increasing use of artificial light at night (ALAN) has led to exposure of freshwater ecosystems to light pollution worldwide. Simultaneously, the spectral composition of nocturnal illumination is changing, following the current shift in outdoor lighting technologies from traditional light sources to light emitting diodes (LED). LEDs emit broad-spectrum white light, with a significant amount of photosynthetically active radiation, and typically a high content of blue light that regulates circadian rhythms in many organisms. While effects of the shift to LED have been investigated in nocturnal animals, its impact on primary producers is unknown. We performed three field experiments in a lowland agricultural drainage ditch to assess the impacts of a transition from high-pressure sodium (HPS) to white LED illumination (color temperature 4000 K) on primary producers in periphyton. In all experiments, we compared biomass and pigment composition of periphyton grown under a natural light regime to that of periphyton exposed to nocturnal HPS or, consecutively, LED light of intensities commonly found in urban waters (approximately 20 lux). Periphyton was collected in time series (1–13 weeks). We found no effect of HPS light on periphyton biomass; however, following a shift to LED the biomass decreased up to 62%. Neither light source had a substantial effect on pigment composition. The contrasting effects of the two light sources on biomass may be explained by differences in their spectral composition, and in particular the blue content. Our results suggest that spectral composition of the light source plays a role in determining the impacts of ALAN on periphyton and that the ongoing transition to LED may increase the ecological impacts of artificial lighting on aquatic primary producers. Reduced biomass in the base of the food web can impact ecosystem functions such as productivity and food supply for higher trophic levels in nocturnally-lit ecosystems.

This paper presents and experimentally applies a research design for studying the temporal dimension of outdoor artificial illumination in complex lightscapes such as those of urban centres. It contributes to filling the gap between analyses of high-resolution aerial imagery, which provide detailed but static information on the spatial composition of lightscapes, and existing methods for studying their dynamics, which measure changes at high levels of aggregation. The research design adopts a small-scale, detailed approach by using close-range time-lapse videos to document the on/off patterns of individual light sources as the night progresses. It provides a framework and vocabulary for discrete and comparative analyses of the identified temporal profiles of lighting. This allows for pinpointing similarities and differences among the dynamics of different places, nights or categories of lighting. Its application to three case studies in Berlin indicate that switch-on and switch-off times are clustered, resulting in static and dynamic phases of the night. Midnight is a temporal fault-line, after which full illumination ends as portions of the illumination are extinguished. Switch-off times and -rates differ among the three lightscapes and, especially, among four functional types of lighting that were differentiated: infrastructural and commercial units largely remain on all night, while substantial portions of architectural and indoor lighting are switched off, though at fairly different times. Such findings are valuable for studies based on data collected at specific points in time (aerial imagery, measurements), for informing and monitoring temporally oriented lighting policies, and for understanding urban dynamics at large.

Artificial nighttime lighting (light pollution) is increasing worldwide and may have undocumented consequences. In this study, we asked if artificial nighttime lighting affects the performance in monoculture of four grass species: the Eurasian Bothriochloa bladhii (Retz.) S.T. Blake (Poaceae), and Bothriochloa ischaemum (L.) Keng (Poaceae); and the North American Panicum virgatum (L.) (Poaceae), and Sorghastrum nutans (L.) Nash (Poaceae). We conducted a field pot experiment to test for the effects of artificial nighttime lighting and plant density on height, biomass, and leaf number. Height of the tallest individual per population was affected by separate interactions between species and density, light, and time. Final total biomass per individual biomass was increased under nighttime lighting, but more so at low density. Leaf number was increased by artificial nighttime lighting irrespective of species. These results suggest that artificial nighttime lighting may have previously undocumented influences on plant height, biomass, and leaf number within certain species. These findings warrant more in-depth studies into the role that artificial nighttime lighting can have on various plant species.

We investigated the toxic effect of visible light on Drosophila lifespan in both sexes. The toxic effect of ultraviolet (UV) light on organisms is well known. However, the effects of illumination with visible light remain unclear. Here, we found that visible light could be toxic to Drosophila survival, depending on the protein content in diet. In addition, further analysis revealed significant interaction between light and sex, and showed that strong light shortened life span by causing opposite direction changes in mortality rate parameters in females versus males. Our findings suggest that photoageing may be a general phenomenon, and support the theory of sexual antagonistic pleiotropy in aging intervention. The results caution that exposure to visible light could be hazardous to life span and suggest that identification of the underlying mechanism would allow better understanding of aging intervention.

The transparent nematode Caenorhabditis elegans can sense UV and blue-violet light to alter behavior. Because high-dose UV and blue-violet light are not a common feature outside of the laboratory setting, we asked what role, if any, could low-intensity visible light play in C. elegans physiology and longevity. Here, we show that C. elegans lifespan is inversely correlated to the time worms were exposed to visible light. While circadian control, lite-1 and tax-2 do not contribute to the lifespan reduction, we demonstrate that visible light creates photooxidative stress along with a general unfolded-protein response that decreases the lifespan. Finally, we find that long-lived mutants are more resistant to light stress, as well as wild-type worms supplemented pharmacologically with antioxidants. This study reveals that transparent nematodes are sensitive to visible light radiation and highlights the need to standardize methods for controlling the unrecognized biased effect of light during lifespan studies in laboratory conditions.